Non-monotonicity in the influence of nanoparticle concentration on SAR in magnetic nanoparticle hyperthermia J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-06-19 Benjamin A. Evans, Matthew D. Bausch, Karl D. Sienerth, Michael J. Davern
Magnetic nanoparticle hyperthermia (MNH) has shown substantial promise as an alternative therapy for deep-tissue tumors or resistant bacterial films. However, while great progress has been made in understanding the physical mechanisms of thermal energy dissipation in MNH, the influence of interparticle magnetic interactions in concentrated solutions remains a substantial challenge limiting progress toward clinical adoption. We have developed a well-dispersed suspension of magnetite nanoparticles which can be varied smoothly with nanoparticle concentrations ranging from 0 to 900 mg/mL. This material serves as a well-controlled experimental model for exploring the role of nanoparticle concentration on heating. We have measured the specific absorption rate (SAR) of the nanoparticles as a function of nanoparticle concentrations up to 320 mg/mL (10% v/v) in applied field frequencies from 86 to 460 kHz. Our results clearly indicate that SAR is non-monotonic with a maximum at concentrations of approximately 1% v/v, in strong agreement with recent theory. In addition, they suggest that optimal concentration is dependent on applied field frequency, and that the exponential dependence of SAR on frequency varies smoothly with concentration. These results provide experimental support for current theoretical efforts and lend insight into new investigations, ultimately leading to better prediction and control of heating in MNH.
Tunable critical temperature and magnetocaloric effect in ternary Prussian blue analogue J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-06-19 Magdalena Fitta, Wojciech Sas, Tomasz Korzeniak
A comprehensive study of structural, magnetic and magnetocaloric properties in the ternary Prussian blue analogue (PBA) Ni1.5[Fe(CN)6]x[Cr(CN)6]1-x∙nH2O (x=0, 0.25, 0.5, 0.75 and 1) is presented. For all compounds the second-order magnetic phase transition from high temperature paramagnetic to the low temperature ferromagnetic state at the Curie temperature (Tc) is observed. We show the possibility of tuning the magnetic and magneto-caloric properties of PBA materials by changing the compositional factor of the metal centres involved in the cyano-bridging. An increase in Fe content leads to increase in the coercive field, whereas the critical temperature decreases from 60 to 22 K. The magnetic entropy change ΔS, as well as the related Relative Cooling Power (RCP), vary with x parameter in the regular way. The highest value of ΔS was observed for sample with x=1 and was equal to 3.49 J mol−1 K−1 under a magnetic field of 50 kOe, whereas the RCP varied from 62 J mol−1 (145.35 J kg−1) to 118 J mol−1 (273.33 J kg−1), when x decreased from 1 to 0.
Peter Grünberg, a great name in the field of magnetism and 2007 laureate of Nobel Prize in Physics passed away on April 7, 2018 J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-06-20 Albert Fert
Development of (Zr,Mn) doped X-type hexaferrites for high frequency EMI shielding applications J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-06-20 Htet Kyaw Ye, S.R. Shannigrahi, C.B. Soh, S.L.W. Yang, L.S. Li, D.V.M. Repka, P. Kumar
X-type hexaferrites with nominal composition of [Ba2(Zr0.5Mn0.5)xFe28-xO44+0.25x] where x = 0, 1.5, 2 and 2.5 were synthesized using solid state reaction technique by applying two different sintering conditions of 1240°C and 1300°C for 5 hrs. Phase pure single phase formation of the synthesized hexaferrites were observed using XRD analysis. Surface morphologies of the sintered polished samples were analysed using SEM and found non spherical grains. The average grain size found to be ∼ 472.9 nm and ∼ 858.11 nm for the samples sintered using the recipe of 1240°C and 1300°C for 5 hrs respectively. Moreover, the grain size increases with the increase of (Zr,Mn) dopant concentration for the samples sintered at 1240°C for 5 hrs and was found decreasing with the increase of (Zr,Mn) dopant concentration for the samples prepared at 1300°C for 5 hrs. The average crystallite size estimated using Scherrer’s formula was in the range of 2.4499 nm and 2.275nm for the samples sintered at 1240°C and 1300°C respectively for 5hrs. Magnetic measurements (M-H) and (M-T) were performed using vibrating sample magnetometer (VSM). Highest remnant magnetization was found for the material (x=2) irrespective of the sintering conditions. Saturation magnetisation was found decreasing with increasing of temperature in all the studied samples irrespective of the sintering conditions. Coercivity (Hc) of all the samples found decreasing with the increase in (Mn,Zr) dopant concentration. Electromagnetic interference (EMI) absorption was determined using E5063A Network Analyser (ENA) with the frequency range of (300MHz-18GHz). The sample Ba2(Zr0.5Mn0.5)2Fe26O44.5 (x=2) sintered at 1240°C, displayed maximum absorption of -36.2dB (99.975%) at 15.4GHz with the bandwidth that indicate frequency range in which RL was more than -20dB (99% absorption) of 0.7GHz (15.1GHz to 15.8 GHz). The rest of the studied samples displayed the bandwidth of 1.2GHz (14.4GHz to 15.6 GHz) for minimum 99% absorption. The sample Ba2(Zr0.5Mn0.5)2Fe26O44.5 (x=2) sintered at 1300°C, displayed maximum absorption of -35.2 dB (99.97%) at 16.8GHz with the bandwidth that indicated RL was more than -20dB (99% absorption) of 1.6GHz (16GHz to 17.6GHz). Zr,Mn doped X-type hexaferrites showed better absorption properties in high frequency range (Ku band (12-18) GHz) and as a result, it can be used for EMI shielding for high frequency applications.
Effect of chemical pressure on physical properties of antiferromagnetic Kondo lattice Ce2Ni3Ge5 J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-06-20 Antu Laha, Z. Hossain
We have studied the enhancement of Kondo scattering in the heavy fermion compounds Ce2Ni3(Ge1-xSix)5Ce2Ni3Ge1-xSix5 by measuring electrical resistivity ρ(T)ρ(T), magnetic susceptibility χ(T)χ(T), isothermal magnetization M(B)M(B), specific heat CP(T)CP(T) and magnetoresistance. All the members of this series crystallize in U2Co3Si5-type orthorhombic structure with space group Ibam. Magnetic susceptibility and specific heat data show that two step antiferromagnetic transitions at x = 0 reduce to a single transition at x = 0.15 followed by a complete suppression of antiferromagnetic ordering at x = 0.20. Positive magnetoresistance below the transition temperature confirms that the transitions are antiferromagnetic up to x = 0.15 and the negative magnetoresistance in the paramagnetic region implies the freezing out of spin-flip scattering in Kondo compounds under the application of magnetic field. Kondo temperature, estimated from paramagnetic Curie temperature and magnetoresistance data, increases with increasing x in Ce2Ni3(Ge1-xSix)5Ce2Ni3Ge1-xSix5forx ⩽⩽0.80. The γγ values also indicate that the Kondo temperature enhances with increasing x after the suppression of antiferromagnetic ordering. Maximum γγvalue (∼∼ 76 mJ mol-1K−2 Ce−1) is observed at x = 0.20 which indicates that the heavy fermion behavior is more pronounced at the magnetic-nonmagnetic boundary. A significant resistivity increase at a particular magnetic field is observed for T = 3.5 K, 3.8 K and 4 K (x = 0 sample) and it is observed for T = 3 K (x = 0.15 sample).
Influence of the two boundaries of the Pt layer on spin current transportation by spin Hall magnetoresistance J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-06-20 Zhiwen Dai, Xiufeng Huang, Dongchao Yang, Lizhi Yi, Fengyu Wu, Hongguang Piao, Liqing Pan
The spin Hall magnetoresistance effects (SMR) in four heterostructures consist of different boundaries of Pt layer has been investigated. The result in this work shows that the two boundaries of Pt layer in all heterostructures both influence the spin current absorption and reflection. The Pt/air interface would weaken the spin current absorption at the Co2FeSi/Pt interface on the other side of the Pt layer. On the contrary, the Pt/MgO(001) interface could boost the spin current absorption strongly at the Co2FeSi/Pt interface on the other side of the Pt layer. And this promotion effect is much stronger than the Co2FeSi/Pt interface on the spin current absorption at the other Co2FeSi/Pt interface. The MgO capping layer may avoid anisotropic magnetoresistance (AMR) induced SMR ratio decreasing at low temperature. This study provides a new way for modulating spin current absorption at the FM/HM interface.
Influence of the low local symmetry of Er3+ ions on magnetic circular dichroism and absorption spectra of f-f transitions in ErFe3(BO3)4 single crystal J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-06-20 A.V. Malakhovskii, V.V. Sokolov, I.A. Gudim
Linearly polarized absorption spectra and magnetic circular dichroism (MCD) spectra of ErFe3(BO3)4 single crystal were measured in the range of 9000 – 23000 cm-1 at 90 K. The absorption spectra of f-f transitions were decomposed into the Lorentz shape components and intensities of the components were found. MCD spectra permitted us to measure the Zeeman splitting of some transitions and so to determine changes of the Landé factor along the C3 axis of the crystal during these transitions. Optical and magneto-optical properties of f-f transitions in the ErFe3(BO3)4 crystal were compared with those in the ErAl3(BO3)4 crystal. Substantial difference of the properties connected with the difference of the Er3+ ions local symmetry in two crystals was revealed. Large splitting of one of the f-f transitions without magnetic field, which is not possible for the Kramers doublets, was observed. It was explained by appearance of two absorbing centers due to the local decrease of symmetry in the excited state. Appreciable difference of the local vibrations energy in some excited states was revealed.
Structural, dielectric and enhanced soft magnetic properties of lithium (Li) substituted nickel ferrite (NiFe2O4)NiFe2O4)nanoparticles J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-06-20 V. Manikandan, Juliano C. Denardin, S. Vigniselvan, R.S. Mane
Li-NiFe2O4Li-NiFe2O4NPs have been prepared by a simple chemical co-precipitation method. The structural analysis of Li-NiFe2O4Li-NiFe2O4nanoparticles with 2-31 nm demonstrates a face centered cubic spinel phase. The scanning electron microscopy and high resolution transmission electron microscopy images highlight moderate good nanocrystalline nature as compared to x=0.4 concentration. The dielectric analysis shows that Li-NiFe2O4Li-NiFe2O4NPs has a high dielectric constant at x=0.2 concentration and then reduced with respect to annealing temperature and concentration. The magnetization curves demonstrate soft magnetic nature where, the saturation and remnant magnetization increases and then coercivity decreases due to increase of annealing temperature and concentration.
What makes magnetic skyrmions different from magnetic bubbles ? J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-06-20 Andrei B. Bogatyrëv, Konstantin L. Metlov
A large enough piece of ferromagnet is usually not magnetized uniformly, but develops a magnetization texture. In thin films these textures can be doubly-periodic. Such are the well known magnetic bubble domains and the recently observed “skyrmion” magnetization textures in MnSi. In this paper we develop a theory of periodic magnetization textures, based on complex calculus to answer the question – is there a difference between those two textures even if they seem to carry the same topological winding number (or topological charge) ? We find that such difference exists, facilitated by a different role played by the magnetization vector’s in-plane phase. We separate classical-like and quantum-like features of magnetization textures and highlight the role of magnetic anisotropy in favouring either of these cases.
Experimental and Theoretical Investigations of Unusual Enhancement of Room Temperature Ferromagnetism in Nickel-Cobalt Codoped CeO2 Nanostructures J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-06-21 Sachin Kumar, Bilal Ahmed, Arvind Singh, Ajeet Singh, Animesh K. Ojha
Room temperature ferromagnetism (RTFM) in Ni/Co codoped CeO2 nanostructures has been studied. The samples are synthesized by hydrothermal method and further characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), Raman spectroscopy (RS), photoluminescence (PL) spectroscopy and vibrating sample magnetometer (VSM) measurements. The undoped CeO2 sample shows RTFM and a consistent enhancement in RTFM is observed after doping. The Ni (5%)-Co (5%) codoped CeO2 nanostructures revealed interestingly, highest RTFM. The origin of RTFM in all CeO2 samples is explained by electronic density of states and magnetic moments calculated using density functional theory (DFT).
Low loss MnZn ferrites for applications in the frequency region of 1-3 MHz J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-06-21 S. Tokatlidis, G. Kogias, V.T. Zaspalis
The purpose of this particular study is the development of a high frequency –1 to 3 MHz- stable MnZn ferrite. The notion under which the study was held was the preliminary investigation of the dissipation mechanisms, and subsequently the hypothesis of the predominance of one. Accordingly the path of enhancement commenced with a selection of high frequency MnZn ferrite as the base –namely one exhibiting high ferromagnetic resonance (FMR) already- and the selective addition of Co2+ and Mg2+. Arguably the offspring of the study was a superb high frequency ferrite, stable throughout the temperature spectrum, 25-115 °C, presenting power losses as low as 87 mW cm-3 (1 MHz, 50 mT, 85 °C) and 319 mW cm-3 (3 MHz, 30 mT, 85 °C). Initial permeability (10 kHz, 0.1 mT) remains higher than the value of 850 (25-115 °C) and FMR appears no earlier than 7.1 MHz. To the authors’ knowledge these values are among the best reported.
Structural, magnetic and microwave absorption properties of SrFe12O19/Ni0.6Zn0.4Fe2O4 composites prepared by one-pot solution combustion method J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-06-21 S.R. Saeedi Afshar, M. Hasheminiasari, S.M. Masoudpanah
SrFe12O19/Ni0.6Zn0.4Fe2O4 powders were synthesized by one-pot solution combustion method. The effects of NiZn ferrite content on phase, structure, microstructure and magnetic properties of composites were investigated by X-ray diffractometry, infrared spectroscopy, electron microscopy and vibrating sample magnetometry techniques. Strontium hexaferrite and NiZn ferrite phases were well crystallized following calcination at 900 °C without any impurities being formed. The powders were composed of platelet-like SrFe12O19 particles being mixed with quasi-spherical NiZn ferrite particles. The composites containing 10 wt. % Ni0.6Zn0.4Fe2O4 exhibited a single magnetization curve with maximum saturation magnetization of 56 emu/g, as a confirmation of exchange coupling, while other composites had “bee waist” type hysteresis loop. The coercivity of composites decreased from 5143 to 1778 Oe with addition of NiZn ferrite phase. The microwave absorption measurements in X-band (8–12 GHz) showed a maximum absorption of -23.5 dB at 9.9 GHz for SrFe12O19-10 wt. % Ni0.6Zn0.4Fe2O4 powders in comparison with the other composites.
Cobalt Spin States Investigation of Ruddlesden-Popper La2-xSrxCoO4, using X-ray diffraction and Infrared Spectroscopy J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-06-21 T. Ghorbani-Moghadam, A. Kompany, M.M. Bagheri-Mohagheghi, M. Ebrahimizadeh Abrishami
Field annealing effect on magnetostriction and sensitivity of the ferromagnetic Fe60Co18Ga22/Si(100) film J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-06-21 S.U. Jen, Y.C. Chen
As-deposit (AD) and field-anneal (FA) Fe60Co18Ga22 films have been made. We found that after FA treatment, both the macro-stress and saturation magnetostriction in the film increase greatly. Also, after FA treatment, the tetragonal L12 phase shows up, and coexists within the original two-phase (A2 + D03) field. In agreement with the theory, the occurrence of large stress and magnetostriction is related to the magnetic-field-induced flip of the tetragonal axis of the L12 phase crystal by FA. As a low-field sensor, FA could enhance the sensitivity of the Fe60Co18Ga22 film element up to 18.9 ppm/Oe.
Enhanced magnetocaloric effect and magnetic properties in Ni47Mn40-xFexIn13 (x = 1, 2) Heusler alloy J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-06-19 S. Arumugam, P. Sivaprakash, S. Esakki Muthu, D.M. Raj kumar, M. Manivel Raja, K. Manikandan, M. Kannan
We report the effect of Fe on the martensitic transitions in Ni47Mn40-xFexIn13 (x = 1 and 2) alloys and associated magnetocaloric effect. Structural and magnetic transitions are observed in x = 1 and 2 alloys. The martensitic transition shifts to low temperature with the increase of Fe concentration. The maximum positive entropy change (ΔSM) with quite large magnitude of 22 Jkg-1K-1 (x = 1) and 51.2 Jkg-1K-1 (x = 2) are observed for a field change of 50 kOe. Substitution of Fe enhances the magnetization as well as increases the ΔSM more than a twice in the x = 2 system.
Direction-dependent electronic phase transition in magnetic field-induced gated phosphorene J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-06-19 H.D. Bui, Mohsen Yarmohammadi
A detailed physical meaning of the electronic phase transition in monolayer black phosphorus (BP) has been addressed in the presence of local gate voltage and Zeeman magnetic field. The main features of this transition characterize within the electronic density of states (DOS) in the vicinity of Fermi level. The numerical calculations have been performed within the continuum approximation of tight-binding model and the Green’s function method. The anisotropy crystal structure of BP causes different behaviors in each component of DOS. First, we have confirmed the Zeeman effect, i.e. the splitting of Van Hove singularities. Then, our results show that the electronic band gap of phosphorene in the x- x - direction in the absence of gate voltage decreases with weak magnetic fields and system transits to the semimetallic phase at strong regimes, whereas there is no phase transition in the y- y - direction. Interestingly, turning on the gate, phase transition independent of the direction does not occur at both weak and strong magnetic fields. Another remarkable point refers to the increase of the band gap with gate voltage at both directions, leading to the semimetallic-semiconductor transition in the x- x - direction at strong magnetic fields. The controllable band gap with the gate voltage and magnetic field quantities are useful for future applications of BP.
Interaction of isolated skyrmions with point and linear defects J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-06-18 Carles Navau, Nuria Del-Valle, Alvaro Sanchez
The dynamic behavior of individual skyrmions is highly affected by the defects in the materials that host them. Here we develop a theory to account for the effect that defects produce over the skyrmion dynamics. The skyrmion-defect interaction mechanism is explained at an atomic level as a local modification of exchange, Dzyaloshinskii-Moriya (DM) and/or anisotropy interaction. Relevant micromagnetic magnitudes as the energy density and effective magnetic fields arising from the presence of the defect are derived. We also find analytical expressions for the forces exerted by this defect over a skyrmion within Thiele’s rigid approximation. Both point-defects as well as linear defects are considered.
Crystalline and magnetic microstructures of iron-rich Sm(Co0.65Fe0.26Cu0.07Zr0.02)7.8 sintered magnets: isothermal aging effect J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-06-18 Kuikui Song, Yikun Fang, Shuai Wang, Nengjun Yu, Hongsheng Chen, Meiling Zhang, Minggang Zhu, Wei Li
Effects of iron nanoparticles’ shape on convective flow of ferrofluid under highly oscillating magnetic field over stretchable rotating disk J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-06-18 Mohsan Hassan, C. Fetecau, Aaqib Majeed, Ahmad Zeeshan
The persistence of the current article is to discuss the iron nanoparticles' shape in flows due to highly oscillating magnetic field over a stretchable rotating disk. For ferrofluid, water is considered as base fluid with suspension of iron nanoparticles having sphere, oblate ellipsoid and prolate ellipsoid shapes with different sizes. The impact of the nanoparticles' shape on velocity and temperature profiles, convective heat transfer coefficient, radial and transverse shear stress is deliberated through graphs and tables. The presence of highly oscillating magnetic field forces the particles to rotate faster than the fluid and, as a result, the total viscosity is certainly reduced. The governing equations, which are firstly modeled and thereafter converted into nonlinear ordinary differential equations in dimensionless form using similarity approach, are analytically solved using the Mathematica package BVPh 2.0 which is based on the homotopy analysis method (HAM).
Equilibrium properties of magnetic filament suspensions J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2017-10-24 Andrey A. Kuznetsov
Langevin dynamics is used to study equilibrium properties of the suspension of magnetic filaments (chains of nanoparticles permanently crosslinked with polymers). It is shown that the filament suspension generally has larger magnetic susceptibility than the system of unlinked nanoparticles with the same average particle concentration. However, actual susceptibility gain strongly depends on length and flexibility of filaments. It also shown that in a strong gravitational (centrifugal) field sedimentation profiles of filaments are less homogeneous than that of unlinked particles. The spatial distribution of filaments weakly depends on the intensity of interparticle dipole-dipole interactions.
Electron and phonon properties of noncentrosymmetric RhGe from ab initio calculations J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2017-10-25 Maria Magnitskaya, Nikolay Chtchelkatchev, Anatoly Tsvyashchenko, Denis Salamatin, Sergey Lepeshkin, Liudmila Fomicheva, Mieczysław Budzyński
Band structure, Fermi surface, and phonon dispersions of noncentrosymmetric B20-type RhGe are calculated ab initio for the first time and their evolution with increasing pressure is investigated. We consider in detail symmetry-conditioned features of the band structure, as well as pressure-induced changes in the Fermi surface topology, which are expected to affect the thermopower of RhGe. We also report on special calculations of electric field gradients on the Rh and Ge nuclei and compare these results with a very recent 111Cd-TDPAC study of B20-RhGe.
Ground state and magnetic properties of the Cr-doped Ni-Mn-(Ga, Ge, In, Sn) alloys: Insights from ab initio study J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2017-10-27 Mikhail A. Zagrebin, Vladimir V. Sokolovskiy, Vasiliy D. Buchelnikov
By using first-principles calculations in combination with supercell approach a series of Ni8Mn2 Cr 2 Z 4 (Z = Ga, Ge, In, Sn) are studied with partial replacing of Mn by Cr to investigate the effect of such substitution on their structural and magnetic properties. Two 16-atom supercells with different distribution of Cr in the Mn sublattice and magnetic ordering are considered. Crystal structure optimization shows that the magnetic ground state of Ni8Mn2 Cr 2 Z 4 (Z = Ga, In) alloys is the state with pairwise antiparallel magnetic moments of Cr atoms. While for Ni8Mn2 Cr 2 Z 4 (Z = Ge, Sn) alloys is it ferromagnetic state with parallel magnetic moments of Cr and Mn atoms. Based on ground state energies it is shown that martensitic phase can be realized only in Ni8Mn2 Cr 2 Z 4 (Z = Ga, Ge) alloys. For the stable crystal structures with associated magnetic order magnetic exchange constants are calculated, to estimate Curie temperatures with the help of mean-field approximation. Obtained results are in qualitative agreement with experimental and theoretical data.
Peculiarities of phonons in Ni-Mn-Ga alloys: Ab initio studies J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2017-10-28 Vasiliy D. Buchelnikov, Olga N. Miroshkina, Mikhail A. Zagrebin, Vladimir V. Sokolovskiy, Christopher K. Pyles, Alexey T. Zayak
This work presents a theoretical investigation of the Heusler compound Ni2MnGa with PHONON and VASP software. In particular, in the focus of this study is the role of the atomic disorder in the phonon instabilities that are characteristic for some Heusler alloys.
Analysis of anomalous negative magnetic contribution to thermal expansion in Sm0.80B6 and pseudobinary compounds Sm1−xLaxB6 (x = 0, 0.10, 0.22, 0.50) J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2017-10-28 D.A. Serebrennikov, E.S. Clementyev, P.A. Alekseev
This study is the first attempt to apply the two-level Weiss model for the invar alloy to intermediate-valence samarium systems. This model is instrumental in giving a quantitative characterisation of the anomalous magnetic contribution to the coefficient of thermal expansion (CTE) of Sm0.80B6 and Sm1−xLaxB6 (x = 0, 0.10, 0.22, 0.50). A good agreement between the experimental and calculated magnetic contributions to the CTE is achieved for Sm0.78La0.22B6 over the temperature range from 0 K to 210 K. In other systems, a good fit is obtained over shorter temperature ranges. The model parameters and the dependence of the CTE minimum on the level of lanthanum doping in SmB6 are presented.
Electrical field control of magnetoelectric effect in composite structures with single crystal piezoelectrics J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2017-11-04 L.Y. Fetisov, D.V. Chashin, D.D. Plekhanova, D.V. Saveliev, Y.K. Fetisov
The influence of constant electric field on the characteristics of the direct magnetoelectric effect in composite structures with single crystal piezoelectric layers was observed. The effect was measured in the structures with langatate and catangasite piezoelectric layers and amorphous magnetic alloy metglas as a ferromagnetic layer. The value of magnetoelectric voltage coefficient of 146 V/(Oe·cm) was obtained for the langatate-based structure and value of 1.35 V/(Oe·cm) for the catangasite-based structure. For the langatate-metglas structure, electrical field of 20 kV/cm resulted in a change in the generated voltage up to 63%, in the quality factor Q up to 76%, and provided linear variation of the resonance frequency up to 16 Hz. Electrical field control of magnetoelectric effect characteristics can be used to design new magnetoelectric devices.
Biomedical applications of glass-coated microwires J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2017-11-06 D. Kozejova, L. Fecova, P. Klein, R. Sabol, R. Hudak, I. Sulla, D. Mudronova, J. Galik, R. Varga
In the given contribution, two examples of applications of glass-coated microwires for biomedical sensing are shown. Firstly, application of microwires for contactless sensing of the intracranial temperature below titanium implants confirms the possibility to sense the temperature with sensitivity down to 0.01 °C. Secondly, application of microwires for monitoring the stress applied on bones after injury or for monitoring the osteomalacy effect is shown. Our measurements confirm that high sensitivity of order of 10−10 s/Pa can be obtained.
Multiferroism and magnetic ordering in new NiBO3 (B = Ti, Ge, Zr, Sn, Hf and Pb) materials: a DFT study J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-06-15 Luis Henrique da Silveira Lacerda, Sergio Ricardo de Lazaro
Multiferroic materials have been investigated as emergent materials to application on new technologies, mainly BiFeO3 material, the most important multiferroic material actually. Others materials reported for multiferroic applications are NiTiO3 and NiPbO3. Therefore, we decide investigate a new series of materials from atoms with d0 and d10 orbitals to avoid magnetic coupling between [NiO6] and [BO6] clusters and to keep a high ferroelectric property .In this manuscript, a DFT/B3LYP investigation was employed to discuss new candidates to multiferroic materials based on NiBO3 (B = Ti, Ge, Zr, Sn, Hf and Pb) compounds in R3c structure. Our results describe as antiferromagnetic states as ferromagnetic states evidencing modifications very interesting on [NiO6] magnetic cluster from perturbation of t2g and eg degenerated energy levels controlled by chemical modifications in [BO6] clusters. The originality of our manuscript is the theoretical evidence that non-magnetic clusters can control the magnetic state of a material from perturbation on energy levels of the magnetic clusters. More amazing is these non-magnetic clusters are also responsible by a high spontaneous polarization naturally found in R3c structures. At end, the multiferroic effect in NiBO3 materials is clarified from coupling between magnetic and ferroelectric properties oriented along z and x directions, respectively.
Enhanced Magnetic Heating Efficiency and Thermal Conductivity of Magnetic Nanofluids with FeZrB Amorphous Nanoparticles J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-06-15 Junzhang Wang, Mingxiu Fan, Xiufang Bian, Mengchun Yu, Tianqi Wang, Shuai Liu, Yinghui Yang, Yuan Tian, Rongzhang Guan
Effect of Y substitution on the structural and magnetic properties of Sm(Fe0.8Co0.2)11.4Ti0.6 J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-06-15 Masaya Hagiwara, Naoyuki Sanada, Shinya Sakurada
The structural and magnetic properties of (Sm, Y)(Fe0.8Co0.2)12-xTix (x = 0.6, 1) prepared by arc melting are investigated. The formation of the ThMn12 structure was facilitated by the substitution of Sm with Y at low Ti concentrations (x = 0.6), and almost a single phase with the ThMn12 structure was obtained for (Sm0.8Y0.2)(Fe0.8Co0.2)11.4Ti0.6. This suggests that Y plays an important role in stabilizing the ThMn12 structure owing to the decrease in the atomic radius of the rare earth site. The intrinsic magnetic properties of (Sm0.8Y0.2)(Fe0.8Co0.2)11.4Ti0.6 exhibited μ0Ms = 1.50 T, μ0Ha = 11 T, and Tc = 820 K at room temperature.
Single-atom vacancy in monolayer phosphorene: a comprehensive study of stability and magnetism under applied strain J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-06-15 Juliana M. Morbec, Gul Rahman, Peter Kratzer
Using first-principles calculations based on density-functional theory we systematically investigate the effect of applied strain on the stability and on the electronic and magnetic properties of monolayer phosphorene with single-atom vacancy. We consider two types of single vacancies: the symmetric SV-55|66 55 | 66 , which has a metallic and non-magnetic ground state, and the asymmetric SV-5|9 5 | 9 , which is energetically more favorable and exhibits a semiconducting and magnetic character. Our results show that compressive strain up to 10%, both biaxial and uniaxial along the zigzag direction, reduces the formation energy of both single-atom vacancies with respect to the pristine configuration and can stabilize these defects in phosphorene. We found that the magnetic moment of the SV-5|9 5 | 9 system is robust under uniaxial strain in the range of -10 - 10 to +10 + 10 %, and it is only destroyed under biaxial compressive strain larger than 8%, when the system also suffers a semiconductor-to-metal transition. Additionally, we found that magnetism can be induced in the SV-55|66 55 | 66 system under uniaxial compressive strain larger than 4% along the zigzag direction and under biaxial tensile strain larger than 6%. Our findings of small formation energies and non-zero magnetic moments for both SV-5|9 5 | 9 and SV-55|66 55 | 66 systems under zigzag uniaxial compressive strain larger than 4% strongly suggest that a magnetic configuration in monolayer phosphorene can be easily realized by single-vacancy formation under uniaxial compressive strain.
A modified residual stress dependent Jile-Atherton hysteresis model J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-06-15 Ronggao Cui, Shuhui Li, Zhe Wang, Xinke Wang
Non-oriented electrical steel is widely used in the manufacturing of motor stators. The magnetic property will be influenced by the residual stress induced from manufacturing processes. The classical Jile-Atherton hysteresis model with constant parameters is widely used to describe the magnetization characteristic of ferromagnetic materials. In the model, the parameter a a represents the domain density, k k is the pinning factor reflecting the strength of the pinning effect, α α is the domain coupling parameter affecting the slope of the mid-segment of the hysteresis loop and C C is the coefficient of reversibility. However, all the four parameters are influenced by residual stress. Furthermore, the influence of magnetic peak induction on parameters can’t be ignored according to our work. The classical Jile-Atherton hysteresis model cannot reflect the influence of residual stress and magnetic peak induction. In this paper, a modified residual stress dependent Jile-Atherton hysteresis model was proposed, whose parameters are extended to functions related to residual stress and magnetic peak induction. A novel device was designed to carry out magnetic property testing experiments under large stress. The parameters were identified by a MATLAB program and the influence of residual stress and magnetic peak induction was analyzed. The accuracy of parameters was validated by experiments, which showed that the modified model worked well in describing the magnetization characteristic under different stresses and magnetic peak inductions. This could provide some guidance for the manufacturing processes of motor stators.
Unusual spin-wave dynamics in core-shell magnetic nanodisks J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-06-15 Huirong Zhao, Ruifang Wang
We investigated the spin dynamics of a vortex state in a core-shell magnetic nanodisk driven by an oscillating field applied perpendicular to the disk plane by means of micromagnetic simulations. The nanodisk comprises a Py (Fe0.2Ni0.8) core of 100 nm in radius, surrounded by a 50 nm thick Fe shell. Fourier transform analyses show that the Py core and the Fe shell dominate spin-wave oscillation at the fundamental and higher order radial modes, respectively. For oscillating driving field tuned to the fundamental eigenfrequency, the Py/Fe interface effectively confines spin-wave excitation in the Py core region. This effect leads to significantly more rapid vortex core (VC) reversal in comparison to homogeneous disks. Our work demonstrates that the higher order modes can drive much faster VC reversal than the fundamental mode, in sharp contrast to the results obtained in homogeneous disks. With excitation levels up to 30 mT, we find strong nonlinear spin-wave dynamics in the system, which results in mode frequency redshifting, therefore the observation of the most rapid VC reversals below eigenfrequencies and VC switching in wide ranges of frequencies.
Exchange bias effect in cylindrical nanowires with ferromagnetic core and polycrystalline antiferromagnetic shell J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-06-14 A. Patsopoulos, D. Kechrakos
We study numerically the exchange bias effect in thin cylindrical nanowires composed of a ferromagnetic core and an antiferromagnetic shell implementing a classical spin Hamiltonian and Monte Carlo simulations. We address systematically the effect of shell polycrystallinity on the characteristic fields of the isothermal hysteresis loop (coercivity, exchange-bias) and their angular dependence upon the direction of the reversing and cooling fields. We relate the observed trends to modifications of the underlying magnetization reversal mechanism. We fit our simulation results to an extended Stoner-Wohlfarth model with effective off-axis unidirectional anisotropy and demonstrate that shell polycrystallinity leads to maximum exchange bias effect in an off-axis direction. Our results are in qualitative agreement with recent experimental studies of Co/CoO nanowires.
Magnetic Properties of Superparamagnetic, Nanocrystalline Cobalt Ferrite Thin Films Deposited at Low Temperature J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-06-14 Neelima Sangeneni, KM Taddei, Navakanta Bhat, SA Shivashankar
Bulk cobalt ferrite, being a hard ferrite, shows high magnetization, high resistivity and high coercivity. If thin films of cobalt ferrite can be deposited at a low enough temperature and if its coercivity can be reduced, cobalt ferrite will make a very good candidate for use as a magnetic core of an integrated inductor in RF-CMOS ICs. Though polycrystalline and epitaxial thin films of cobalt ferrite have been made by various techniques, there are no reports of thin films of superparamagnetic cobalt ferrite. In this work, nanocrystalline cobalt ferrite thin films, which are superparamagnetic as deposited, have been prepared in the solution medium at ∼190°C, using microwave irradiation. The as-prepared films have a saturation magnetization (MS) of 401 emu/cc and coercivity (HC) of 19 Oe at room temperature for a crystallite size of 2 nm. The cobalt ferrite powder obtained as a by-product during the same process has MS of 50 emu/g and HC of 5 Oe at room temperature, making it superparamagnetic. The as-prepared films were annealed in air at 300°C for 5 min and 10 min. Annealing for 10 min results in an increase in crystallite size to 36 nm, MS increases from 401 emu/cc to 545 emu/cc, and HC increases from 19 Oe to 860 Oe. The change in magnetic properties can be directly associated with change in the crystallite size and degree of crystallographic inversion, as determined by neutron diffraction and deduced from X-ray photoelectron spectroscopy.
Magnetic and structural properties of L10 Mn-Ga epitaxially grown islands J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-06-14 Siqian Zhao, Yoshitomo Tanaka, Takuya Sato, Keisuke Kamiya, Gary Mankey, Takao Suzuki
Magnetic and structural properties of L10 Mn53Ga47 islands epitaxially grown onto MgO(100) substrates are discussed. The samples were fabricated by sputter-deposition at a substrate temperature Ts during deposition. The samples deposited at Ts above 500 oC were found to form the island structure of Volmer-Weber type. The average size of the islands fabricated at Ts = 600 oC is around 200 nm in width and 60 nm in height. The XRD and TEM analyses indicate that those islands are of the L10 phase with the <001> axis perpendicular to the substrate surface. The lattice constants a and c are 3.91±0.01 Å and 3.65±0.02 Å, respectively, which are larger by 0.8%, and smaller by 1.5% respectively, as compared to the bulk values of the same composition. The order parameter of these islands is found to increase from 0.7 to 0.8 for Ts = 450 to500 oC, and then remains nearly constant (≈ 0.8) for higher Ts. The M-H hysteresis loops exhibit a high squareness for all the samples for Ts = 450∼600 oC. The saturation magnetization Ms is about 220 and 350 emu/cm3 for Ts = 450 and 600 oC, respectively. The out-of-plane coercivity Hc is 5 and 13 kOe for Ts = 450 and 600 oC, respectively. The temperature dependence of Ms for the sample made at Ts = 600 oC was measured and fitted to an empirical relation in order to estimate Tc. The estimated Tc around 600 K is in reasonable agreement with the reported value of bulk L10 Mn53Ga47. The uniaxial perpendicular magnetic anisotropy constant Ku estimated by the out-of-plane torque curves is around 1.1×107 and 8.3×106 erg/cm3 at 5 and 300 K, respectively. The initial magnetization curves of these islands exhibit a typical pinning mode for the coercivity mechanism. A phenomenological discussion of the coercivity is presented on the basis of Kronmuller’s formula. It is found that the coefficient α and effective demagnetizing factor Neff in the formula by Kronmuller are approximately 0.38 and 12. For the magnetic anisotropy mechanism, the power law relation between Ku(T) and Ms(T) is examined. It is found that the exponent n for Ku(T)∝Ms(T)n varies from 2.3 to 3.5 for T from 350 to 5K. However, the n in a whole temperature range from 5 to 350 K is 2.6. The n = 2.6 suggests a deviation from the single-ion mechanism, and is consistent with the theoretical predictions of Ga contribution.
Eu valence transition behavior in the nano form of EuPd2Si2 J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-06-14 Kartik K Iyer, Tathamay Basu, P.L. Paulose, E.V. Sampathkumaran
The compound EuPd2Si2 is a well-known fluctuating-valent compound with a largest variation of Eu valence in a narrow temperature interval (around 150 K). The ball-milled form of this compound was investigated to understand the Eu valence behavior in the nanoform. The compound is found to retain the ThCr2Si2-type tetragonal structure after ball-milling leading to a reduction in particle size, typically falling in the range 10 – 100 nm. We find that there is a qualitative change in the temperature dependence of magnetic susceptibility for such small particles, with respect to that known for bulk form. To understand this microscopically, Mössbauer spectra as a function of temperature were taken. The Mössbauer spectra of the nanocrystalline compound is essentially divalent-like at room temperature, but becomes distinctly bimodal at all temperatures below 300 K, unlike that of the bulk form. That is, there is a progressive transfer of intensity from divalent position to trivalent position with a gradual decrease of temperature. We attribute it to a first-order valence transition, with extreme broadening by defects in the nano specimen. Thus there is a qualitative change in the valence behavior in this compound as the particle size is reduced by ball-milling. Such a particle size study is reported for the first time for a Eu-based mixed valent compound.
Structural, magnetic, magnetocaloric and critical Behavior studies in the vicinity of the Paramagnetic to Ferromagnetic Phase Transition Temperature in LaMnO3+δ LaMnO 3 + δ Compound J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-06-13 Mazhar Iqbal, Muhammad Nasir Khan, Ayaz Arif Khan
This article comprises of the structural, magnetic, magneto-caloric and critical behavior study of single phase perovskite manganite LaMnO3+δ sample synthesized by traditional Solid State route. X-ray powder diffraction (XRD) at room temperature indicates the single phase trigonal crystalline structure of LaMnO3+δ with hexagonal setting R 3 ‾ c . Magnetic, magnetocaloric and critical behavior are studied using temperature dependent magnetization (M-T) and applied magnetic field dependent magnetization (M-H) data probed by Physical Property Measurement System (PPMS). The second order ferromagnetic to paramagnetic (FM-PM) phase transition is observe at Curie temperature (TC∼180K). This phase transition is responsible for maximum entropy change ( Δ S M max ) of 0.451(1) J/kg K at applied magnetic field of 6 Tesla with relative cooling power (RCP) of 54.293(5) J/kg. At TC, the order of magnetic phase transition is examined by employing Modified Arrott plots (MAP), Kouvel Fisher (KF) and simple isotherm analysis technique. The obtained values of critical exponent’s β ≈ 0.365±0.06, γ ≈ 1.14±0.04 and δ ≈ 4.16±0.10 elaborate that the magnetic phase transition coordinated well with the 3D-Heisenberg model at TC ≈ 180 K and are confirmed by scaling equations of state. Similarly the change in magnetic entropy (ΔSM) versus applied magnetic field recorded complies with the power law ΔS = (H) n with n = 0.64 at TC = 180K.
Dependence of the demagnetization behavior on the direction of grain boundary diffusion in sintered Nd-Fe-B magnets J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-06-11 Fugang Chen, Tieqiao Zhang, Wenhao Zhang, Lanting Zhang, Yunxue Jin
The effect of the direction of coercivity distribution gradient on the demagnetization behavior of anisotropic sintered Nd-Fe-B magnets was investigated via both experiments and simulations. In the grain boundary diffusion process (GBDP) using Dy70Cu30, the magnet diffused parallel to the c-axis shows much higher squareness factor (Hk/Hcj, 0.92) than that diffused perpendicular to the c-axis (Hk/Hcj, 0.83). To simulate the different gradient of coercivity distribution with respect to the c-axis after the GBDP, composite Nd-Fe-B magnets composed of two different grades of Nd-Fe-B magnets were fabricated via diffusion bonding. The anisotropic demagnetization behavior of the composite magnets sandwiched in two directions is similar to that of the magnets after GBDP along two perpendicular directions. Micro-magnetic simulations further confirmed the dependence of demagnetization behavior on the direction of coercivity distribution gradient with respect to the c-axis. For the magnet with the direction of coercivity distribution gradient parallel to the c-axis, the initial demagnetization needs to overcome a much higher energy barrier than that perpendicular to the c-axis. It indicates that the gradient of coercivity distribution induced by GBDP parallel to the c-axis is much more effective to save the usage of heavy rare earth elements than that perpendicular to the c-axis.
Magnetic skyrmion size and stability in ultrathin nanodots accounting Dzyaloshinskii-Moriya exchange interaction J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-06-07 A.R. Aranda, A. Hierro-Rodriguez, G.N. Kakazei, O. Chubykalo-Fesenko, K.Y. Guslienko
The stability of the skyrmion magnetization configurations in ultrathin circular magnetic nanodots is calculated analytically and simulated micromagnetically considering realistic magnetic and geometrical dot parameters taken from recent experiments. The chiral Dzyaloshinskii-Moriya exchange interaction (DMI) is taken into account as an interfacial energy term. The diagram of single Néel skyrmion stability/metastability, skyrmion sizes and magnetization profiles are found as a function of the magnetic and geometrical dot parameters. It is shown that most of skyrmions are unstable or metastable and the stability region where the Néel skyrmion is the ground state is small. The Dzyaloshinskii criterion for the instability of ferromagnetic state in bulk ferromagnets with respect to the increasing DMI strength should be essentially modified to describe the stability of magnetic skyrmions in 2D systems like ultrathin ferromagnetic films and nanodots.
Mechanochemically Processed Zinc Ferrite Nanoparticles: Evolution of Structure and Impact of Induced Cation Inversion J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-06-06 Vincent G. Harris, Vladimir Šepelák
Among the many types of preparation techniques, the non-conventional mechanochemical processing has been recognized as an alternative route to nanomaterials. It is integral to the preparation of ceramic materials, including magnetoceramics, such as spinels, garnets, and hexaferrites, among others. This technique imparts copious levels of kinetic energy through collisions of balls, chamber walls, and media particles resulting in not only physical mixing, attrition, and solid state reaction, but also vacancies, strain, and cation inversion. Here, we strive to elucidate the impact of mechanochemical processing upon a single step solid-state reaction and the inversion of cations in the zinc ferrite system and their impact upon important long-range magnetic properties of volumetric magnetization, Néel temperature, and nuclear magnetic properties, including hyperfine field distributions, isomer shifts, and quadrupole interactions.
Phase diagrams and magnetic properties of a ferrimagnetic Ising bilayer superlattice: A Monte Carlo study J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-06-06 Dan Lv, Wei Wang, Jin-ping Liu, De-qiang Guo, San-xi Li
Monte Carlo simulation has been used to study the magnetic and thermodynamic properties of a ferrimagnetic mixed spin-1 and spin-3/2 Ising bilayer superlattice system on the honeycomb structure. The ground state phase diagrams of the system have been obtained for different single-ion anisotropies and exchange couplings. The system exhibits characteristic critical behaviors such as compensation points, the first- and second-order phase transition points as well as the tricritical points. The effects of the single-ion anisotropies and the exchange couplings on the magnetization, the susceptibility, the internal energy, the specific heat and the hysteresis loops are discussed in detail. Lots of interesting magnetic phenomena have been found, originating from the competitions among the anisotropies, the exchange couplings, the temperature and the external magnetic field. In particular, multiple cycle hysteresis loops behaviors such as the double and triple hysteresis loops have been discovered. Our results are in excellent agreement with previous theoretical studies.
Analysis of phase composition of LiZn and LiTi ferrites by XRD and thermomagnetometric analysis J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-06-05 E.N. Lysenko, A.L. Astafyev, V.A. Vlasov, A.P. Surzhikov
In this work, the method of quantitative ferrite phase control, which is based on thermomagnetometric analysis of the ferrite samples in magnetic field, was developed. The magneto-phase transitions in LiZn and LiTi ferrites with chemical formulas Li0.5(1x)Fe2.50.5xZnxO4 and Li0.5(1+x)Fe2.51.5xTixO4 were studied, and their phase compositions were analyzed by both the developed method and X-ray diffraction analysis. It was shown that the thermomagnetometry method compared to X-ray diffraction analysis allows to examine more precisely the magnetic phases in synthesized ferrites with inhomogeneous phase composition. However, a complex analysis, using both X-ray and thermomagnetometry methods, will be the most optimal in case of the formation of non-magnetic and poor magnetic phases.
Rheological response of magnetorheological suspensions sediments and its implications for redispersibility J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-06-05 Fang-Hao Niu, Zhi-De Hu, Hua Yan, Jian-Jian Yang, Han-Song Zhang
This work reports an investigation into the redispersibility of magnetorheological suspensions (MR suspensions) by testing the rheological properties of suspension sediment. By using a new freeze-sampling method, slices of sediment were taken from the bottom of the container with little changes on shear history which makes it possible to employ rheological measurement. Size distribution of particles contained in sediment was studied by a laser scattering method. Oscillatory and steady shear was employed to studying the rheological viscoelastic and flow behavior. Also, thixotropy and recovery behavior was also studied. The results obtained proved that redispersibility is a multifactor-dependent property which can be reflected from rheological responses of MR suspensions’ sediment. Hydrodynamic force and particle interaction which have significant influence on those properties were analyzed in this study. In addition, indexes correspond to different rheological properties were put forward to make a comparison quantitatively between traditional MR suspensions.
Influence of quadratic Zeeman effect on spin waves in dipolar lattices J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-06-05 V.I. Yukalov, E.P. Yukalova
A lattice of particles with dipolar magnetic moments is considered under the presence of quadratic Zeeman effect. Two types of this effect are taken into account, the effect due to an external nonresonant magnetic field and the effect caused by an alternating quasiresonance electromagnetic field. The presence of the alternating-field quadratic Zeeman effect makes it possible to efficiently vary the sample characteristics. The main attention is payed to the study of spin waves whose properties depend on the quadratic Zeeman effect. By varying the quadratic Zeeman-effect parameter it is possible to either suppress or stabilize spin waves.
Domain-wall-assisted giant magnetoimpedance of thin-wall ferromagnetic nanotubes J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-06-05 Andrzej Janutka, Kacper Brzuszek
We study the efficiency of the magnetoimpedance (MI) of thin-walled circumferentially-ordered nanotubes in sub-GHz and GHz frequency regimes, using micromagnetic simulations. We consider empty ferromagnetic tubes as well as tubes filled with non-magnetic conductors of circular cross-section (nanowire coverings), focusing on the low-field regime of MI (below a characteristic field of the low-frequency ferromagnetic resonance). In this field area, the efficient mechanism of MI is related to oscillations of the positions of (perpendicular to the tube axis) domain walls (DWs). Two mechanisms of driving the DW motion with the AC current are taken into account; the driving via the Oersted field and via the spin-transfer torque. The simulations are performed for Co nanotubes of the diameter of 300nm. Achievable low-field MI exceeds 100%%, while the field region of a high sensitivity of that DW-based giant MI is of the width of tens of kA/m. The later is widely adjustable with changing the density of the driving AC current, its frequency, and the nanotube length. Of particular interest is the resonant motion of DW due to the interaction with the nanotube ends, the conditions of whom are discussed.
Saturation Magnetization Studies on Iron-Nickel Ball Milling Nanopowders and Spark Plasma Sintered Specimens J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-06-05 T. Ashokkumar, A. Rajadurai, Gouthama, Subash C.B. Gopinath
Saturation Magnetization (Ms) is one of the important states among all magnetic properties, it decides the materials can be either used as a hard or soft magnet. Mechanical alloyed and spark plasma sintered at the promising levels of 40, 50 and 75 wt.% Ni-Fe have been investigated to find out the Ms with the effect of the composition, grain size, particle size and extent of alloying. This study revealed that the value of Ms is increased due to the formation of a Ni3Fe compound, and it dependent on the grain size. The introduction of the Ni3Fe compound was confirmed by X-ray diffraction analysis. It was found that ambient temperature played a critical role in sintering Ni-Fe alloy. The value of the Ms is found to be high at the intermediate particle size and become lower when the particle size is either large or small. From this study, it was cleared that preparation of Ni-Fe alloy under the right temperature with the proper grain size favours for the potential downstream applications and generation of light materials.
Investigating the Electric and Magnetic Transport Properties of Na0.5Bi0.5TiO3 – BaFe12O19 Nanocomposite System for Magnetoimpedance Sensor Application J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-06-05 Ranjit Pattanayak, Surya Prakash Ghosh, Subhajit Raut, Sourav Kuila, Simanchalo Panigrahi
Structural and magneto-transport properties of Mn1+xCo1-xSn (x = 0.0-1.0) alloys J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-06-05 Ishfaq Ahmad Shah, Guizhou Xu, Najam ul Hassan, Muhammad Arif, Yurong You, Jun Liu, Yuanyuan Gong, Xuefei Miao, Feng Xu
Hexagonal MnMX alloys present interesting properties like non-collinear magnetism, reentrant spin glass, novel skyrmion-domain formation, etc. In this work, we synthesized Mn1+xCo1-xSn (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) alloys using arc melting and melt spinning techniques. A pure Ni2In-type structure was obtained in alloys of x = 0.4-0.8. The lattice parameters increase systematically with an increase in the Mn content. ZFC-FC measurements show reentrant spin-glass-like and non-collinear magnetic transition, reflecting the competition of several exchange interactions. The magnetic properties also show strong dependence on the anti-site disorder. First-principles calculations are applied to explain the evolution of the magnetic state. The magnetoresistance values for all alloy ribbons are negative and linearly changed, dominated by the spin-dependent scattering. Both magnetoresistance and anomalous Hall effect show hysteresis at low temperatures, consistent with the magnetization measurements.
Structural, electronic and magnetic properties of the manganese telluride layers AMnTe2 (A=K, Rb, Cs) from first-principles calculations J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-06-04 A. Benmakhlouf, Y. Bourourou, A. Bouhemadou, A. Bentabet, F. Khemloul, S. Maabed, M. Bouchenafa, I. Galanakis
Using first-principles electronic structure calculations based on density functional theory (DFT), we investigate the structural, electronic and magnetic properties of the layered ternary manganese tellurides: AMnTe2 (A = K, Rb, and Cs). Calculations are accomplished within the full-potential linearized augmented plane wave (FP-LAPW) using the generalized gradient approximation GGA formalism for the exchange correlation term. We have treated all ferromagnetic, antiferromagnetic and non-magnetic phases and found that the ferromagnetic is the ground-state for all studied compounds. Moreover, all three compounds under study are half-metals with a total spin magnetic per formula unit of 4μBμB which is mainly localized at the Mn atoms. We express for these compounds a new version of the Slater-Pauling rule and discuss in detail the origin of the minority-spin gap. Finally, we have also calculated some other relevant quantities such as the bulk modulus B, the pressure derivative B’, the virtual semiconducting gap Eg, and the half-metallic gap EHM.
Renormalized Gaussian approach to size effects and exchange interactions: application to localized ferromagnets and amorphous magnets J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2018-06-04 R.M. Keumo Tsiaze, A.V. Wirngo, S.E. Mkam Tchouobiap, E. Baloïtcha, M.N. Hounkonnou
This paper gives a model field-theoretic description of thermodynamic magnetization fluctuations and exchange interactions in localized ferromagnets and amorphous magnets. A local Ginzburg-Landau type Hamiltonian is used to describe the properties observed in the transition region. The approach provides another method of tackling interacting spin systems dominated by size effects, fluctuations and correlations, which lead to a dimensional phenomenology of critical behavior. It is also found that the competition between long- and short-range interactions gives rise to the redistribution of the density of spins and causes the anisotropy of the electron spectrum. Above the upper-critical dimension, the approach behaves like mean-field theory with however, thermodynamic quantities modified by intrinsic critical fluctuations, whereas it predicts correctly the universal quantities for dimension 4 and below. At all temperatures, the model matches the magnetic observables, thus providing a unified picture for both the Gaussian and critical regimes.
FMR investigations of exchange biased NiFe/IrMn/NiFe trilayers with high and low Ni relative content J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2017-11-07 Irina O. Dzhun, Georgy V. Babaytsev, Nikolay G. Chechenin, Christina A. Gritsenko, Valeria V. Rodionova
Magnetic properties of trilayer double-exchange biased Si/Ta(30 nm)/NixFe(1−x)(10 nm)/IrMn(tAF)/NixFe(1−x(10 нм)/Ta(30 нм) thin film structures with x = 0.4 and x = 0.75 were investigated. The exchange bias, noncollinearity of unidirectional and uniaxial anisotropy and magnetization in both bottom and top ferromagnetic layers as a function of the antiferromagnetic (AF) layer thickness in the range from 2 to 50 nm were investigated. The obtained effects support the model of ferromagnetic coupling through the antiferromagnetic spacer and the model of rotatable anisotropy contribution at small AF thickness. It was found that usage of low-nickel permalloy in exchange biased systems has advantages of higher magnetization, a higher magnetic ordering at the interface and smaller critical thickness of antiferromagnetic layer to set the exchange bias, though provides a lower exchange bias compared with normal permalloy composition.
Magnetocaloric effect and magnetostrictive deformation in Tb-Dy-Gd-Co-Al with Laves phase structure J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2017-11-07 G.A. Politova, N.Yu. Pankratov, P.Yu. Vanina, A.V. Filimonov, A.I. Rudskoy, G.S. Burkhanov, A.S. Ilyushin, I.S. Tereshina
The influence of partial substitution of Co by Al atoms on the magnetocaloric and magnetostrictive properties of the multicomponent Tb-Dy-Gd-Co compounds with a Laves phase structure was investigated. The samples were obtained by arc melting using of high-purity rare-earth metals. The crystal structure of Tb 0.2 Dy 0.8 - x Gd x Co 2 - y Al y (x = 0.3, 0.4, and 0.5; y = 0 and 0.1) compounds was monitored by powder X-ray diffraction. The magnetostriction and the magnetocaloric effect in external magnetic field up to 12 and 18 kOe, respectively, were studied in wide temperature range. The Curie temperature of Al-content compounds increases by an average of 20 K, while the magnitudes of the magnetocaloric effect and the magnetostriction slightly decrease.
Magnetic properties of Fe100−xGax: Ab initio and Monte Carlo study J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2017-11-08 Mariya V. Matyunina, Mikhail A. Zagrebin, Vladimir V. Sokolovskiy, Vasiliy D. Buchelnikov
This work presents a theoretical study of magnetic properties for Fe 100 - x Ga x (x = 25, 28.125%) alloys in the framework of first-principles calculations and Monte Carlo simulations. In particular, the zero-temperature ground state properties, magnetocrystalline energy, and magnetic exchange coupling constants for both D03 and L12 structures are calculated. It is shown that for both structures, the magnetocrystalline anisotropy energy change the sign from positive to negative during tetragonal distortion from c / a < 1 to c / a > 1 , respectively. Using the exchange interaction constants within Heisenberg model, the thermomagnetization curves and Curie temperatures for compositions studied are obtained. Calculated data are in a good agreement with experimental ones.
Synthesis of FeNi tetrataenite phase by means of chemical precipitation J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2017-11-10 Vladislav L. Kurichenko, Dmitriy Yu. Karpenkov, Alexey Yu. Karpenkov, Marina B. Lyakhova, Vladimir V. Khovaylo
FeNi L10 (tetrataenite) phase has great perspectives for hard magnetic materials production. In this paper we report on synthesis of this phase in chemically co-precipitated FeNi nanopowder by means of a thermal treatment procedure which includes cycling oxidation and reduction processes at 320 °C. The presence of the FeNi L10 phase in the samples was confirmed by magnetic measurements and differential scanning calorimetry analysis.
Magneto-optical properties of nanocomposites ferromagnetic-carbon J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2017-11-12 Elena Gan'shina, V. Garshin, N. Perova, G. Zykov, А. Aleshnikov, Yu Kalinin, A. Sitnikov
Current work is devoted to the study of magneto-optical properties of ferromagnetic metal-carbon nanocomposites that belong to a new class of composites in which partial mixing and the formation of metastable phases between components are allowed. Films of nanocomposites were obtained using ion-beam sputtering of composite target on ceramic substrates. There were three systems synthesized with wide range of magnetic phase concentrations – (Co40Fe40B20)X(SiO2)100−X(1), (Co401Fe40B20)X(C)100−X(2)and (Co)X(C)100−X (3). It is found that the evolution of the TKE spectra for the [(Co)x (C)100−x] system with a change in the concentration of FM granules indicates a transition from amorphous CoC granules to crystalline Co granules in a carbon matrix. The shape TKE spectra for the system2 was weakly dependent on the concentrations x. The difference in the behavior of the magneto-optical properties of the [(Co)x (C)100−x] and [(Co40Fe40B20)x(C)100−x] system is explained on the basis of the composite formation model, taking into account the possibility of chemical reactions of carbon with metals and boron.
Modeling of the structural and magnetic properties of Fe-Rh-(Z) (Z = Mn, Pt) alloys by first principles methods J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2017-11-14 Oksana O. Pavlukhina, Vladimir V. Sokolovskiy, Mikhail A. Zagrebin, Vasiliy D. Buchelnikov
The structural and magnetic properties of Mn- and Pt-doped Fe-Rh alloys are investigated by first principles calculations. The 16-atom supercell (Fe8 Rh 8 - x Z x ) with different initial spin configurations including ferromagnetic and two types of antiferromagnetic orders are considered. It is shown that in a case of Fe8 Rh 8 - x Mn x , the ferromagnetic spin configuration in a cubic cell is energetically favorable compared to other magnetic configurations. The addition of Mn content stimulates the martensitic transformation from ferromagnetic cubic phase to antiferromagnetic tetragonal one. Moreover, an increase in Mn content leads to increase in the energy difference between cubic and tetragonal phases which is equivalent of increase in a temperature of structural transformation. Contrary, for Fe8 Rh 8 - x Pt x , an increase in Pt content results to appearance of stable tetragonal state with the checkerboard-like antiferromagnetic configuration.
Cooling rate upon in air heat treatment and magnetic properties of amorphous soft magnetic alloys J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2017-11-15 N.A. Skulkina, O.A. Ivanov, N.D. Denisov, V.I. Chekis
Investigation of the cooling rate effect during heat treatment in air of amorphous magnetic alloys of Fe-Ni-Si-B and Co-Fe-Ni-Cr-Mn-Si-B in states with different signs of saturation magnetostriction were performed to optimize the magnetic properties. It is shown that the increase in cooling rate from 15 to 40 °C/min contributes to the magnetic properties improvement in a state with λs > 0 and their deterioration in a state with λs < 0. This is due to the different influence of induced stresses caused by interaction of ribbon surface with atmospheric water vapor, and their value changes affected by cooling rate change.
Ternary diagrams of magnetic properties of Ni-Mn-Ga Heusler alloys from ab initio and Monte Carlo studies J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2017-11-15 Vladimir V. Sokolovskiy, Yulia A. Sokolovskaya, Mikhail A. Zagrebin, Vasiliy D. Buchelnikov, Alexey T. Zayak
A systematic ab initio calculations based on the DFT methodology and Spin-Polarized Relativistic Korringa-Kohn-Rostoker method are carried out to investigate magnetic properties of structure-disordered Ni-Mn-Ga Heusler alloys. In order to generate a complete set of disorder compositions, which will cover the whole area of the ternary diagram of Ni-Mn-Ga, the coherent potential approximation is used. Using our previously calculated lattice constants, the magnetic moments and exchange coupling constants are calculated for the optimized crystal structure of selected alloys. Obtained data from ab initio calculations are used as input for Monte Carlo simulations of Heisenberg Hamiltonian to compute the thermomagnetization curves. The Curie temperatures for the austenite structure of studied compositions are obtained and mapped onto the ternary diagram. The calculated data for Ni-Mn-Ga are in a good agreement with available experimental ones.
Non-equilibrium critical dynamics of multilayer magnetic structures J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2017-11-21 Pavel V. Prudnikov, Vladimir V. Prudnikov, Alexandr N. Purtov, Marina V. Mamonova, Natalia I. Piskunova
The Monte Carlo simulation of the critical behavior of multilayer structures based on anisotropic Heisenberg model is performed. The analysis reveals aging effects characterized by a slowing down of the relaxation and correlation characteristics in the system with the waiting time. The dependence of aging characteristics on thickness of ferromagnetic films is investigated. The investigation of non-equilibrium critical behavior of multilayer structure which correspond to the nanoscale superlattice Co/Cu/Co demonstrates that the aging effects can be observed in a wider temperature range than for bulk magnetic systems.
Novel models of magnetic dynamics for characterization of nanoparticles biodegradation in a body from Mössbauer and magnetization measurements J. Magn. Magn. Mater. (IF 2.63) Pub Date : 2017-11-22 M.A. Chuev
We discuss ways of an improvement of the analytic technique for characterization of magnetic nanoparticles and their chemical transformation to ferritin-like forms after their injection in a living organism by means of measuring and analyzing the Mössbauer spectra and magnetization curves. This is based first on the theoretical achievements in developing models of magnetic dynamics of antiferromagnetic nanoparticles for describing thermodynamic properties of ferritin and related proteins. Generalization of the approach for ferrimagnetic nanoparticles allows one to take directly into account the magnetic nature of nanoparticles in analyzing the corresponding experimental data. Another way is to extend this technique with measuring and analyzing non-equilibrium magnetization curves (hysteresis loops) which allows one to more reliably evaluate time changes in the residual nanoparticles and iron-containing proteins characteristics during biodegradation.
Some contents have been Reproduced by permission of The Royal Society of Chemistry.
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